How do ageing and dominance changes affect the acoustic structure of fallow buck groans? [abstract]

Sexually selected vocalisations of males often provide accurate information about individual identity and quality. Age related morphological changes affecting sound production may also cause modifications of vocalisations, as for humans. Vocalisations can thus potentially be used by other males or by females to assess male body size, dominance status or even age. Fallow buck groans are produced for a short period each year during the breeding season. Previous studies showed that the acoustic structure of groans is individualized and signal body size and dominance status. Groans are also not stable and throughout the breeding season, within-individual changes in call structure potentially signal fatigue and loss of body condition. A question which has not yet been investigated is whether the vocal identity of individuals changes between years, because of changes in dominance status, age and the long period in between breeding seasons during which males are silent. We investigated this by analysing age and rank effects on the acoustic structure of groans of the same males recorded during consecutive years. We expected some changes in call structure as males began to senesce. We also predicted that acoustic parameters related to the status of individuals should change from year to year, because of the known changes in rank as males get older. The potential of groan structure to signal identity and quality and to change as males of a long-lived social mammal get older have important implications for both intrasexual and intersexual communication.